Magnet for cathode-ray tube ion traps



Oct. 2, 1951 J. DE LEON 2,569,517

MAGNET FOR CATHODE-RAY TUBE ION TRAPS Filed Sept. 9, 1949 INVEN TOR.JOHN DE LEON B P fVp ja Patented Oct. 2, 1951 2,569,517 MAGNET FORCATHODE-RAY TUBE ION TR APS John de Leon, Ridgewood, N. 1., minor toAllen B. Du Mont Laboratories, Inc., Pasaaic, N. J., a corporation ofDelaware Application September 9, 1949, Serial No. 114,722

8 Claims. 1

This invention relates to cathode ray tubes such as are used intelevision apparatus and to means for preventing ion blemishes in thefluorescent screens thereof.

Although in the manufacture of cathode ray tubes for television, greatcare is exercised to obtain a high vacuum, nevertheless during usenegative ions often appear in minute quantities. In an electrostaticdeflection cathode ray tube these ions are deflected with the negativeelectrons and hence do not concentrate in one spot. In a magneticallydeflected cathode ray tube, however, since the negative ions areconsiderably heavier than the electrons, the former are not appreciabldeflected, and hence often concentrate in one portion of the fluorescentscreen, causing a blemish to appear.

An object of this invention is to provide a magnetic structureparticularly adapted to be used as a part of an ion trap.

Another object is to provide a magnetic structure which can readily andadequately compensate for structural variations in the electron gun of acathode ray tube.

Another object is to provide a magnetic structure not requiringelectrical connections.

Other objects can best be understood by referring to the accompanyingdrawings in which:

Fig. 1 shows in perspective one embodiment of my invention;

Fig. 2 shows in perspective another embodiment of my invention;

Fig. 3 shows the structure of Fig. 1 is use to prevent ion blemishes ina cathode ray tube, parts being broken away for clarity of illustration.

Referring to Fig. 1, a permanent magnet I2 is fastened to two soft ironpole pieces i3 and H by means of non-magnetic sheets l5 and I5. Bypeening or spreading the tips I! of these sheets l5 and I6 afterassembly, the entire structure is held together. The other ends of thepole pieces 13 and I 4 are held together in a manner known to the art bya brass screw 23 and a thumb nut 24, forming a clamp that holds thestructure to the neck of a cathode ray tube. The word soft here is beingused to denote the property of being readily magnetized, such as ischaracteristic of soft iron, cold rolled steel, and silicon steel,distinguishing thereby from "hard or permanent magnetic materials whichresist magnetization and demagnetization, examples being cobalt steelsand Alnico.

A magnetic shunt member ll of soft magnetic material is attached at itscenter to one of the 2 sheets is by means of a rivet I 9 so as to berotatable, a spring 22 providing friction therefor,

The operation of the magnetic structure is as follows: Magnetic flux,having as its source the permanent magnet, extends along the pole piecesin the direction of the clamping screw 23 and extends across the spacebetween the pole pieces l3 and H as shown by the dotted line 25.Although a single dotted line is shown for illustrative purposes, theflux actually is distributed quite uniformly over the area between thepole pieces, this area being occupied by the neck of a cathode ray tube.

In addition, some of the flux from the permanent magnet I 2 extendsalong the pole pieces in the other direction and bridges the shortdistance to the shunt member I8 as shown by a second dotted line 26. Byrotating the shunt member I8, the reluctance of the second flux path 26can be controlled. If the reluctance of this second path is low, moreflux will pass therethrough and less flux will pass along the first path25 through the neck of the cathode ray tube.

A second embodiment of my invention, similar to that shown in Fig. 1, isshown in Fig. 2. However, in contrast to that embodiment shown in Fig.l, the magnetic shunt member 21 comprises magnetic material in acylindrical form having a threaded opening extending longitudinallyalong its axis. The shunt member?! is supported on a magnetic clampingscrew 3| having corresponding threads. This screw 3| is provided with abridging structure 28, the tips 29 of which fit into slots 32 on theedges of the pole piece I3. A hole 33 in the pole piece l3 providesclearance for the shunt 21.

In Fig. 3, a cathode ray television picture tube is shown with themagnetic structure H of Fig. 1 in place of the neck of the tube, part ofone of the pole pieces being broken away, however, so that the electrongun structure of the tube is clearly visible. This gun consists of athermionic cathode 34, providing a source of electrons, a controlelectrode 35 controlling the intensity of the beam, and a bent anodestructure 36 providing acceleration of the beam 3'1. The gun parts arecontained in an evacuated envelope 38, preferably glass, along with afluorescent screen 39, these parts being well known to the art.

The magnetic structure H, which has already been described in detail inconnection with Fig. 1, provides a magnetic field 25 at right angles tothe axis of the tube, the strength of the field being adjustable bymeans of the magnetic shunt l8.

The action of the magnet is to deflect the electrons in the regiondesignated by the reference numeral 43. The electrons are emitted fromthe cathode 34 and are accelerated in a path forming an angle with theaxis of the tube. In the region 43 the electrons are bent by themagnetic field into a beam 37 which is parallel to the axis of the tubeand centered therewith. Being thus bent the electrons pass through asmall hole 44 in the end of the accelerating anode 36. The negativeions, following the same path from the cathode, are not appreciablydeflected by the magnet because of their far greater mass and follow astraight course 45 so that instead of being emitted from the hole 44they are trapped" within the accelerating anode structure 35 and do notstrike the fluorescent screen 39.

Because of the variations in the mechanical and electrical properties ofthe electron gun and associated portions of the cathode ray tubestructure in production, it is desirable that the magnetic field 25 beadjustable. In this way the ion trap magnet can be adjusted for eachtube so that the beam is centered properly on the hole 44. In thisinvention this adjustment can be made by the adjustable magnetic shuntprovided for the purpose.

Although the specific embodiments of my invention have been shown anddescribed the scope of my invention can best be understood by thefollowing claims.

What is claimed is:

1. A magnetic structure for producing a magnetic field in an areacontaining an electron beam, comprising a source of magnetic flux, polepieces of soft magnetic material and respective opposite polarityattached thereto, extending respectively along opposite sides of andbeyond said area,

and lying substantially in a plane normal to said beam and an adjustablemagnetic shunt member positioned between and bridging a portion of thedistance between said pole pieces outside said area.

2. A magnetic structure for deflecting the beam of a cathode ray tubecomprising two pole pieces of soft magnetic material and respectiveopposite polarity, shaped to fit about and extend beyond the neck ofsaid cathod ray tube on respective opposite sides thereof and lying in aplane normal to the longitudinal axis of said beam. a source of magneticflux attached to and extending between said pole pieces, and a magneticshunt of soft magnetic material positioned between and bridging aportion of the space between, the extension of said pole pieces.

3. An electron beam deflecting structure comprising two pole pieces ofrespective opposite polarity and of soft magnetic material, lying in aplane normal to the longitudinal axis of said beam, having complementarysemi annular portions and laterally extending portions, a permanentmagnet connected to and extending between said pole pieces, and amagnetic shunt of soft magnetic material positioned between saidlaterally extending portions of said pole pieces to bridge a portion ofthe space therebetween.

4. An electron beam deflecting structure comprising two pole pieces ofsoft magnetic material of respective opposite polarity lying in a planenormal to the longitudinal axis of said beam, having semi annularlyshaped portions and laterally extending portions, a source of magneticflux extending between said pole pieces and a pivotally mounted shunt ofsoft magnetic material bridging by an adjustable amount the spacebetween said laterally extending portions of said pole pieces.

5. An electron beam deflecting structure for a cathode ray tubecomprising two pole pieces of soft magnetic material shaped to flt aboutand extend beyond the neck of a cathode ray tube, a source of magneticflux extending between said pole pieces, a bridge of non-magneticmaterial extending between the extension of said pole pieces, and amagnetic shunt of soft magnetic material afiixed to said bridge.

6. An electron beam deflecting structure comprising two pole pieces ofsoft magnetic material having complementary semi annular portions andlaterally extending portions, a source of magnetic flux attached to andextending between said pole pieces, a bridge of non-magnetic materialextending between said laterally extending portions of said pole pieces,and a magnetic shunt of soft magnetic material secured rotatably to saidbr dge.

7. An electron beam deflecting structure comprsing two pole pieces ofsoft magnetic material having complementary semi annular portions andlaterally extending portions, a permanent magnet attached to andextending between said pole pieces, a threaded screw of non-magneticmaterial extending between and connecting said laterally extendingportions of said pole pieces and a sleeve of magnetic material mountedon said screw and positioned between said pole pieces.

8. An electron beam deflecting structure for a cathode ray tubecomprising two pole pieces of soft magnetic material shaped to fit aboutand extend beyond the neck of a cathode ray tube, a permanent magnetattached to and extending between said pole pieces, a threaded screw ofnonmagnetic material connecting the extension of said pole piecesproviding means for clamping said magnet to said neck, and a sleeve ofmagnetic material mounted on said screw, said sleeve being threadedinternally and extending at least partially through one of said polepieces.

JOHN M: LEON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,181,850 Nlcoll Nov. 28, 19392,211,613 Bowie Aug. 13, 1940 2,234,720 De Tar Mar. 11, 1941 2,274,586Branson Feb. 24, 1942 2,416,687 Fry Mar. 4, 1947 2,418,487 Sproul Apr.8, 1947 2,431,113 Glyptis et al Nov. 18, 1947 2,456,474 Wainwright Dec.14, 1948 2,460,609 Torsch Feb. 1, 1949 2,472,766 Woodbridge June 7, 19492,499,065 Heppner Feb. 28, 1950 2,500,455 Fisher Mar. 14, 1950 2,513,929Gethmann' July 4, 1950 2,522,872 Heppner Sept. 19, 1950 2,539,156Ostreicher Jan. 23, 1951 2,542,924 Heppner Feb. 20, 1951 FOREIGN PATENTSNumber Country Date 464,637 Great Britain Apr. 21, 1937

